1. Field of the Invention
The present invention relates to positive drive differentials of a type which drive either or both of a pair of drive axles, while permitting free overrun of either axle.
2. Brief Description of the Prior Art
A common type of positive drive differential long known in the prior art is that which has a basic configuration comprising an outer drive casing, having flattened or rounded cam or drive surfaces, two axially aligned inner hubs each engaging a respective drive axle, and a roller clutch assembly positioned around the hubs so as to be interposed between the hubs and the drive casing. There are two sets of roller clutch elements, each set being mounted in a respective roller cage, which keeps its roller elements properly positioned around the periphery of the hub. The two cages are interlocked in a manner to provide limited relative rotation of the cages so that one of the hub members is permitted to overrun, without causing the roller elements of the overrunning member to lock up in the opposite direction and thus prevent the free overrun.
For proper operation of this type of positive drive differential, there must be some frictional means provided between the roller cage assembly and the inner driven hub members, so that the cage assembly tends to rotate with the hub members rather than the drive casing, this being necessary for proper clutching engagement of the drive casing with the hubs. Also, for operation of the differential without "clutch chatter", there should be frictional means between the driven hub members and the drive casing itself. This particular phenomenon of clutch chatter is described in detail in the Weismann et al. patent, U.S. Pat. No. 3,283,611. This patent shows a positive drive differential wherein friction between the cage and the driven member is provided by wire springs which are mounted in the cages and press against the driven members. In this Weismann et al. patent, frictional engagement between the driven hub members and the drive casing is accomplished by placing spring means between the two driven hubs, which press the hubs axially outwardly against the drive casing.
To cite other examples of the prior art, U.S. Pat. No. 3,581,597, Reiersgaard, provides friction means between the two cages and the driven hubs by a first set of O-rings, and friction between the cages and the drive casing by means of a second set of O-rings. U.S. Pat. No. 3,447,396, Seliger, also provides two sets of O-rings for frictional engagement, but the second set of O-rings provides friction between the drive casing and the driven hub. U.S. Pat. No. 3,700,082, Schwab, illustrates a positive drive differential where the two cages have inwardly extending radial flanges positioned at a location axially outwardly from the two driven hub members. A pair of spring loaded friction plugs mounted in the two hub members press outwardly against the two cage flanges to press these two cage flanges against the drive casing. Thus there is frictional engagement from the driven hubs to the cages, and from the cages to the drive casing.